Hardcopy devices, such as photocopiers, scanners and printers, are capable of reproducing color images from color documents and photographs. To reproduce the color images, the images from the color documents or photographs are sensed and reproduced based upon tri-stimulus values, whose amplitude is proportional to radiance, but whose spectral composition is carefully chosen according to the principles of color science. Tri-stimulus values in typical imaging systems are represented as red, green and blue (RGB), which are linear light values. In the typical imaging systems, the RGB tri-stimulus values are subjected to a nonlinear transfer function, such as gamma correction, that mimics the lightness response of vision. The resulting non-linear light values may be represented as R′G′B′ tri-stimulus values.
A digitized color image is represented as an array of pixels, where each pixel contains numerical components that define a color. The systems that may be used for image coding include the linear RGB and nonlinear R′G′B′ systems described above. Other image coding systems include nonlinear cyan, magenta and yellow (CMY), nonlinear CMY and black (CMYK), and derivatives of these coding systems. Cyan with magenta produces blue, cyan with yellow produces green and yellow with magenta produces red. The CMY values are typically derived from the RGB or R′G′B′ values, and the K value is typically derived from the CMY values. After an image is scanned, RGB data is generated and can be converted to CMY data and/or CMYK data.